Barnum's stock

Moderesa de Beagá

What kind of stock is this sentence talking about?
P.T. Barnum was an expert at destroying his competitor’s reputation. He published letters in newspapers, warning the public against buying his opponent’s stock. He was a master at poking mockery at the tactics of his rivals.

I know this character, Barnum, but have no idea of which stock is implied here:

livestock? merchandise? Well there are so many alternatives...
There is also these illustrations, but I still can't figure it out which stock it does speak about.

Senior Member

As Rover says, it could mean shares in a company owned or run by the opponent. It could also be a synonym for the opponent's plausibility, so that it would mean "warning the public not to be fooled by his opponent's plausibility"